1. Field of the Invention
The present invention relates to a voltage regulator.
2. Description of the Related Art
A conventional voltage regulator will be described with reference to FIG. 2.
FIG. 2 is a circuit block diagram showing an example of a configuration of the conventional voltage regulator.
As shown in FIG. 2, a voltage regulator 201, which is provided with external terminals, namely, an input voltage terminal 102, a GND terminal 103 and an output voltage terminal 104, is constituted by a reference voltage circuit 105 capable of outputting a constant voltage, a voltage dividing circuit 106 capable of dividing in an appropriate proportion a voltage of the output voltage terminal 104, an error amplifier circuit 107 capable of comparing two input voltages to adjust an output voltage, and an output circuit 108 capable of adjusting an impedance.
The error amplifier circuit 107 causes the output circuit 108 to adjust an impedance such that an input voltage from the voltage dividing circuit 106 is kept equal to an output voltage of the reference voltage circuit 105. Therefore, the voltage regulator 201 can keep a voltage of the output voltage terminal 104 constant even if an input voltage fluctuates.
In FIG. 2, the voltage dividing circuit 106 is constituted by resistors, and the output circuit 108 is constituted by an enhancement PMOS transistor. Various external loads such as a CPU and a microcomputer are connected to the output voltage terminal 104 according to an application of the voltage regulator 201. The voltage regulator 201 generates in the output circuit 108 a loss represented by the following expression (1).
Pt=(Vinxe2x88x92Vout)xc3x97Ioutxe2x80x83xe2x80x83(1) 
Where Pt is a loss (W), Vin is an input voltage (V), Vout is an output voltage (V) and Iout is an output current (A).
When the input voltage is high and the output current is large (an impedance of an external load is low), the loss increases. Usually, an allowable loss is defined for a plastic package or the like in which a voltage regulator is implemented and a user sets conditions of use not to exceed the allowable loss. Most of the loss is generated in the form of heat.
However, in the conventional voltage regulator, if it is erroneously used in excess of an allowable loss, there are problems that characteristics of the voltage regulator are deteriorated and the regulator may be destroyed by generated heat. Thus, a user is required to a measurement for heat radiation and safety in order to cope with a case of the voltage regulator being erroneously used in excess of an allowable loss.
In order to solve the above-described problems, a voltage regulator of the present invention is provided with means for detecting a loss, with which the voltage regulator can detect an increase in a loss to automatically enter a protective operation and reduce the loss.
The voltage regulator of the present invention is provided with a loss detecting circuit that functions so as to lower an output voltage when a loss has increased. When the loss detecting circuit is activated, the output voltage falls to decrease an output current, reducing the loss. As a result, an automatic protective function against an excessive loss is added to the voltage regulator, whereby a voltage regulator with high safety can be realized in which its characteristics are not deteriorated and the regulator is not destroyed even if conditions of use are erroneously set.
According to the present invention, there is provided a voltage regulator comprising:
an error amplifier circuit that receives an output from a reference voltage generation circuit as one input;
an output circuit that is controlled by an output of the error amplifier circuit;
a voltage dividing circuit that is connected to the output circuit in series, the error amplifier circuit receiving a divided voltage from the voltage dividing circuit as the other input;
a first loss detecting circuit that is connected between the one input of the error amplifier circuit and a GND terminal; and
a second loss detecting circuit that is connected between an input voltage terminal of the output circuit and an output terminal of the error amplifier circuit.
Here, as the loss detecting circuit, there may be used a temperature detecting circuit in which a gate and a source of an enhancement PMOS transistor are electrically connected or a temperature detecting circuit in which a gate and a source of an enhancement NMOS transistor are electrically connected.